Composition



May 19,1942. NEIMAN 2,283,611

COMPOSITION Filed March 4, 1941 T/IE/ZM/IL EXPANSION IN PER CENT o 300400 1300 800 I000 I200 I400 I600 I600 TEMPERATURE m DEGREES F.

Tql

SETTING EXPANSION lN PER CENT 0 0 4o-eo-z 4 8 16 32 64 TIMEJN MINUTESTIME IN HOURS.

- l I INVENTOR.

ROBERT NE/MA N,

Mamie Attorney Patented May 19, 1942 UNlTED STATES PATENT oFFm a2,283,611 a coMrosrnoN- Robert Neiman, Louisville, Ky., assignor toEdmund A. Steinbeck, l iouisvllle, Ky.

Application March 4, 1941, Serial No. 381,709

' Claims. (Cl. 22- 188) This invention relates to compositions thatbecome plastic when gaged with aqueous solutions, and may be formed intoa desired shape and size and thence set to av hard cementitious masssuitable for dies, counter-dies, patterns, molds for casting metals,etc., all of which must conformwith great exactness to a predeterminedsize,

- shape, and detail.

Thisinvention will be described in detail with regard to its applicationin making dental castings, such as inlays. This is an example of a typeof casting which must be very accurately made as far as size and shapeare concerned,,

After the investment sets the 'mold is heated to a temperature of 800 F.to 1800 F., in order to melt and burn out the wax, and also to preparethe mold for casting. Any suitable or desirable casting method may thenbe employed.

Usually, use is made of some machine which forces the molten metal,under pressure, into, the I cavity formerly occupied by the wax. Themold is then usually cooled by plunging it into water, it is then brokenapart to recover the casting.

The casting is then cleaned, sprues removed,-

and polished for use.

o It is the general practice in most industries to enlarge the originalpattern so as to take care of the casting'shrinkage of the metal. Sincethis is practically impossible or very 'diflicult when using a waxpattern another method must be used. Inthis instance and in order tomake the castingconform to .a predetermined siz'e and shape, that is, tothe original pattern,.lthe mold is caused to expand sumciently, prior tothe casting operation, to counteract the shrinkage of the metal oralloythat takes'place when the lattercools and solidifies during thecasting process. This shrinka e'to be counteractedgenerallyvaries from-'about 1% to. somewhat over 12%, depending ion the size and shape of thecasting, and especially onthe type of casting alloy used. For dentalcastings, using precious alloys, it varies from about 1% to 1.5generally There are a number of iactors which control the exact amountof expanslonnecessary'. The

shrinkages in the process are incurred-.whenthe wax pattern is removedfrom the human-mouth at 95 F. and taken'in a room ofvarying-temperature, but generally cooler than the mouth.

gagin water.

The metal upon casting shrinks, and a'precious dental alloy gives auniform casting shrinkage of 1.25%. To counteract these shrinkages, one

which is uniform and the other which varies due to diiferent conditions,it is necessary to vary the expansion of the mold. The principalexpansion is achieved through the thermal expansion of the investmentmold upon heating from room temperature to casting temperature,generally about 1300 F. Furthermore, the investment expands during thesetting reaction of the binder. The following is a list of the importantfeatures and properties which the dental profession heretoforeespecially has desired in a commercial investment and mold producedtherefrom.

1. The thermal expansion of .the mold from room temperature to castingtemperature (of the mold) should be as nearly as possible equal to thetotal shrinkage encountered and preferably be attained by an investmentmix of painting or pouring consistency.

2. Practically all of the expansion should have taken place at 1150 F.with no radical change thereafter up to at least 1300 F.

3. There should be little variat-ionin expansion due to the usual slightvariation in amount of 4. The thermal expansion curve,.throughout theentire heating range, should approximate a straight line and preferablyshould never rise above the practically straight line curve of theencircling metallic ring or container-of approximately equal totalexpansion.

'5. The investment should incorporate readily with water and mix to asmooth, creamy consistency which can readily be applied to the intricatesections, of a wax pattern and should have a good adherence to thewaxpatt'ern.

'6. Should have enough setting expansion to make an accuratereproduction which is usually about 0.1%. l I

- 7. Should setrapidly to a hard mass that will withstand rapid heatingto the casting' -temp'eratures without cracking or distorting.

' 8. Whenonce set, the mold should not change "chemically or physicallyor distortappreciablyin any deleterious way.

9. Should pos'sessenoughjstrength when at the casting temperature tosafely resist the inrush of molten alloy under casting pressure andnot-too strong to prevent its being easily removed from the castingafter quenching inwater and without leavinga tenaciously'adhering filmon the casting. I

' 1 10. The mold should be very'smooth and of. such chemical makeup asto prevent undue oxidation and'sulfurization of the casting, andpreferably should produce the cleanest possible smooth and densecasting.

' binder.

aaeaen surface so as to produce the smoothest, densest,

and least contaminated, castings possible. Such materials includeaccelerators, retarders, reducing agents (such as carbon or graphite)flne clay, powdered metals, and oxides, as well as other modifyingagents to reduce the amount of gaging .water necessary, such aspolysaccharides and alhas a testing or pouring consistency of 60 partsof water to 100 parts .of plaster by weight. An-

other form of hemihydrate, known as alpha gypsum, (United States PatentNumber 1,901,051) and commercially known as I-Lvdrocal," general- 1y hasa testing or pouring consistency of approximately 40 parts of water to100 parts of alpha gypsum. This lower consistency is ad-. vantageous inincreasing-the expansion and also the strength 'of the mold. There areseveral other forms of calcium sulfate, such as, for example,dehydrated-hemil'iydrate and Keenes cement, both hydrated anddehydrated, that set when gaged with water, and may also act as a Theterm calcium sulphate or calcium sulphate binder will be usedhereinafter to cover high thermal expansion, it is obvious thatrefractory fillers with inherent high expansion properties are to bepreferred. Silica, in its three principal modifications, quartz,tridymite,

and cristobalite, possesses high thermal expansion along with goodrefractory properties and in addition is fairly inexpensive. The Quartzform is tlfe'least expensive and most generally used. Of the threeforms, cristobalite has the greatest inherent thermal expansion and whenused to replace an'equal amount of. quartz will impart a greaterexpansion to the mold in direct proportion to the amount used.

Many other types of refractories may be used to replace all or part ofthe silica and include, for example, such common and widely used,inexpensive refractory materials as magnesia, alumina, chromium oxide,refractory clays, and many other silicates and oxides. Other commonsilicates and oxides have high expansions due to change of phase orinversion. They may be used advantageouslyas partor all of therefractory filler. l e

' The term refractory filler when used here- V inafter shall beconstrued to include any of the above mentioned refractories alone or inany mixture thereof, or any similar materials having substantially thesame property of being fairly inert chemically and withstanding thetemperatures encountered in the casting process and which are compatiblewiththe other ingredients present.

In addition to the binder and refractory filler, it is desirable to addone or more of the following agents to adjust the setting or hardeningcharacteristics, improve the smoothness or permeability of the mold orotherwise to impart desirable physical or chemical action to the moldwith the accompanying drawing, forming a part pattern method that willattain the desired kali.

ample, a mixture of 30 parts Hydrocal, 69

parts powdered quartz, and 1 part modifying agent and being gaged with32 parts of water will showvn expansion of .74% at 1300 F, A number of.materials are known that will increase the thermal expansion of such amixture when added thereto or used in replacing part of the quartz orfiller. Materials of this nature include boric acid, cristobalite,chlorides, (such as sodium, potassium, and lithium) also organiccarboxylic and polycarboxylic acids. Each of these, or combinationsthereof, are of particular value in increasing the expansionsuponheating, but each of them fails to meet one or more of the elevendesired properties or meets them but partially. All of the elevendesirable qualities are met by investment compositions made inaccordance with the disclosure in prior patent application filedFebruary '7, 1936, Serial No. 62,801 for Investments, but thesecompositions do not always successfully operate at, so called, highheats, that is, above 1350" F.

Dueto the difficulty of getting high thermal expansion in an amountsuiiicient to counteract the metal casting shrinkage plus wax patternshrinkage it has been believed desirable to provide investments withadditional considerable setting expansion. Also, no means. was known toreduce the setting expansion when found unnecessary. This practiceresulted in mold distortion due to unequal radial and vertical expansionin a partially confining mold forming member, such as the usual metallicring..-

All of the foregoing difliculties have been overcome by the investmentof this invention.

It is therefore the principal objective of this invention to provide acomposition for m I refractories and an investment composition for usein casting. principally by the disappearing wax tures described above.

in an investment composition for making molds an expansion controlwhereby other desirable features will be attained, as will behereinafter more fully described, above the already mentioned elevenfeatures.

Other objects and advantages of this invention should be readilyapparent by reference to the following specification, considered inconjunction thereof, and it is understood that any modifications may bemade in the exact proportions set forth within the scope of the appendedclaims and without departing from or exceeding the spirit of theinvention.

In thedrawing: Fig. 1 is a graph illustrating the thermal ex pansion ofthree investment compositions each of different constituents when heatedunder identical conditions.

Fig. 2 is-a graph illustrating the setting'expension ofthree investmentcompositions each The above simple type of investment compotheseingredientsas just set forth may be varied beyond these limits,depending upon the exact technic used in producing castings.

In Fig. 1 of the drawing the reference numeral l indicates the thermalexpansion curve of a mixture of 30% alpha gypsum, 69% quartz andapproximately 1% of modifying agents as generally used in the art, andindicates the thermal expansion of 124% between room temperature and1300 F- This investment was made with a water to powder ratio (W/P) of.32, that is, 32

parts of water to 100 parts of powder mixture on a weight basis. Anincrease of the W/P ratio causes an appreciable decrease in the thermalexpansion of this type of mixture. It should be vestments containing thelast named expansion improving agents have a failing in that they showconsiderable shrinkage at'temperatures in excess of approximately 1350F.

It will be noted, therefore, the curve ll begins to show a shrinkage atapproximately 1350 F.

and which shrinkage becomes quite pronounced.

' above 1400" F. It has been found that all other noted, however, that,while the converse'is true and also while the W/P ratio could belowered, from a commercial standpoint this particular .W/P ratio is veryexcellent for a painting composition or mixture, that is, theconsistency-is very suitable for painting onto the wax pattern.

In Fig. 1 of the drawing, the curve indicated by reference numeral II,shows the thermal expansion resulting from a modificationof the simpleinvestment composition (curve 10) by adding to said simple investmentcomposition 1.75%, by weight, of barium chloride for a similar amount ofquartz. In this composition, the W/P ratio was held the same as above,that is, .32. As is readily apparent this resulted in a thermalexpansion of 1.20% between room temperature and 1300 F. By comparison ofthe curves l0 and II it will be noted that the barium chloride producedan investment composition that was, throughout the heating range fromroom temperature to 1300 F., expanding regularly while the simpleinvestment composition expanded, contracted slightly and thenre-expanded. In commercial practice, especially on comparatively largemolds, there is often a temperature differential of several hundreddegrees between different parts of the molds. Ob-. viously, if one-partis expanding and another standing still or contracting slightly,distortion and cracking often takes place. Such distortion, etc.,' oftenoccurs when using the simple investment composition, while, in themodified comsoluble chlorides, as have been clearly disclosed v anddescribed in the co-pending application above identified, act similarly.These chlorides, similar to barium chloride, have the tendency ofbreaking or shrinking at temperatures comparative to that of said bariumchloride. It is the property of these chlorides, however, to give veryclean castings of precious alloys when cast at the usual castingtemperature of 1200 to 1300" F.

As was noted above, other thermal expanding improving agents have beenemployed but none of these have s'ofar been as successful for inlaycastings as the one whose curve is'shown in curve H and which investmenthas best met the requirements in practical use and is the only one Ithat meets all of the eleven desirable features to the greatest extent.

It has beenv found that the shrinkage which occurs in the compositionthat gave curve ll may best be overcome by the use of cadmia cadmiumoxide), Curve l2 in Fig. 1 illustrates the position, such danger ispractically eliminated.

It should be noted'that precious alloys, as used in dentistry and whencast in a mold at 1300 F., have a casting shrinkage of 1.25%. The bariumchloride investment, as shown in curve H, has

an expansion of 1.20% at this casting temperature. This is practicallysufiicient for counteracting the casting shrinkage of the metal.

Thermal expansion improving agents such as disclosed in co-pendingpatent application, above identified, with barium chloride as'the bestexample, enable investments to be made that will meet all of the elevenabove named heretofore desirable features. Due, however, to the in-,creasing use of electrically heated furnaces, many of which have nomeansfor accurately controlling the 'upper temperature limit, as a means forheating investments, the above mentioned inshrinkage occurs.

tremendous advantage to be gained by the addition of as little as 1% ofcadmia. It must also be noted that as little as 0.1% will be quitehelpful and, in fact, any appreciable addition of cadmia increases thethermal expansion range seemingly out of proportion to the small amountsused and cadmia has been found to be the most powerful such agent knownon a weight basis. To give an equal amount of increased thermalexpansion above 1350 F. and prevent the breakdown, the best heretoforeknown agent has beenpowdered metallic-copper, but it willtakeapproximately 5% of it to equal the improvement given by 1% of cadmia.

It also seems that where air is passed over the mold and a slightlyoxidizing condition is present that copper loses some of itseffectiveness, whereas under similar conditions cadmia is substan tiallyunimpaired.

It seems that, perhaps, the most effective amount of cadmia to be addedto the composition giving curve II is 1%*=thereof.

not appreciably further raise the thermal expansion curve. As a matterof fact, increased raise the temperature at which even slight Amounts inexcess of about 2% of cadmia gives a practically straight line curvefrom1200 F. to 1800 F. and even higher.

Upon running a thermal expansion test of'the composition giving curve IIthe iron-constantan thermocouple wires used were completely deterioratedby the decomposition gases, which very likely includes those of chlorineand sulphur at about1350 F., the temperature at'w'hich shrinkage began.With the addition .of 1% of cadmia forming the investment giving curve12 a number of expansion tests were made with the same size and grade ofthermocouple wires which did not deteriorate until a temperature'of 1500to 1550 F.'was reached. It thus seems that the decomposition productsare absorbed or adsorbed by the cadmia. This is further accentuated bythe fact that deleterious fumes are noticeable in Increased amounts ofcadmia above approximately1% do .present conditions to the bestadvantage.

the laboratory at the respective temperatures at aase'p'n gmost'desirable type ofsmoothcleanpastings and which the thermocouplewires are destroyed by the compositions with and without the addition ofcadmia. It is known that cadmia will form a very stable sulphide and,perhaps, this explains whythe expansion properties are improved and theshrinkage range extended to higher tempera-e tures. This is probably dueto the reaction 01.

the cadmia with the decomposing sulphur prodagents. They do however,shrink at the higher temperatures. In general the soluble bromides givegreater expansion and are useful at higher temperatures than thecorresponding chlorides,

see co-pending application Serial No. 293,448, filed September 9, 1939.In turn the soluble iodides give greater'expansion and are useful athigher temperatures than thebromides, see 00- pending application SerialNo. 293,449, filed September 9, 1939. All soluble nitrates alsoconsiderably improve the thermal expansion properties,

some of them, for example, ammonium nitrate are even more effective thanthe iodides at. the higher temperatures, see co-pending application,Serial No. 297,723, filed October 3, 1939. It has also been found thatsolublech'romates, chlorates,

bromates, iodates, borates, phosphates, sulphates, and also the ites ofall these, and even organic salts, acids and alkalies, which is alsotrueof the inorganic group, will also improve the thermal expansionproperties at some temperature or The advantages of one over the otheroften depend upon the desired features and upon the technicused. Thechlorides, for example, generally achieve the full thermal expansion atabout 1150 Band then remain constant untilabout 1300 tog 1400 F.,depending upon the nature of the filler, etc., and then begin to shrinksome slightly, for example, sodium chloride, but most "of them givecurves similar to curve ii.

The bromides increase the temperature at which shrinkage begins, theiodides further raise 1% or cadmia. does not interfere with" thisalready highly desirable property? There is reason to believe thatcastings made above 1325"" F. in

the presence or cadm ia are somewhat better than those-made inthe-compositions without it, such as curve ll composition and this isprobably explained by the removal of at least some of thedeleteriousdecomposition produced by the cadmia.

Soluble chlorides, when added in amounts of. 1 to 2% to the basiccomposition (as shown in Fig. 1), will providecurves of greaterexpansion than the latter, but. show shrinkage at higher temperatures.with thesesoluble chlorides the addition of about 1% of cadmia will givean investment whose thermal expansion curve is of the type as shown incurve l2 and which curve is, perhaps, the most desirable possible for aninvention to be used in the casting of precious metaldentalrestorations. It reaches the most desirable figure of 1.25%thermal expansion at the most desirable casting temperature ofapproximately 1300 F, and, in fact, castings may be made in thiscomposition that will be extremely accurate whether they be made at1150" F. or at any temperature up to-1800' F. Thus the only detriment ofthe composition, which developed curve H to prevent its exceeding all ofthe eleven desirable characteristics is efi ectively overcome.

Cadmia lends similar improvement to other chlorides, for example,ammonium, copper, cadmium and nickel. Allof th'ese, especially copper,

'give a curve showing tremendous shrinkage between 1325" F. and highertemperatures and.

of cadmia is less pronounced in raising the shrinkage temperature, buthas been found of at least some advantage.

it and the nitrates, especially ammonium, seen: u

to raise it the most, that is, give the steepest rise in curve from 1100F. up to approximateiyv 1800 F. The latter type giving a steep riseenables the user to achieve the desired expansion by controlling thecasting temperature and choosing that temperature at which the invest-1200 F. and under such conditions the chlorides,

especially the one shown in curve ii, meets 0bviously; where the castingtemperature cannot be controlled, and there are numerousi'urnaces'thatarein this category, such as the uncontrolled electric, type furnaces,above indicated, the

- shrinkage that takes place, and which begins at approximately 1350 F.for the particular composition shown, is detrimental and is. perhaps,the only detrimental feature found when compared with other present-dayinvestments.

As mentioned heretofore, chlorides give the As already explained, cadmiaisespecially effective in raising the decomposition temperature,

or temperature at which shrinkage begins, in

compositions containing soluble chlorides. In

addition, cadmia seems to absorb a considerableamount of thedecomposition products given ed in investments due to the heating andcontaining soluble chloride. With those expansion improving agents thatin themselves cause expansion to take place to-temperatures approaching1800 F.- the improving eiTect of cadmia is less pronounced. The moreeffective the thermal expansion improving agent is in maintaining arising curve above 1200 F. the less pronounced the efiectiveness ofcadmia in improving this effect. It still seems, however, to beefiective in, absorbing deleterious decomposition products, even thoughthese do, not cause shrinkage to take place.

To help counteract shrinkages, in addition to that of casting shrinkage,especially that of the wax pattern, the setting expansion of investmentshave heretofore been believed to be of advantage. The-usual settingexpansion of an investment is about 3% and all of the importantinvestment compositionson the market show M 2,288,611 found and desired,it has been the consensus of experts that the effective settingexpansion is as unpredictable as its cause is unexplainable.

Most inlay castings are made by investing the wax pattern on a sprueformer while held inside a confining metallic ring. Theoretically, thesetting expansion of an investment cannot take place radially, since themetallic confining ring will resist such an attempt. Assuming that allof the setting expansion takes place, it must, therefore, take placevertically, that is, in a-direction perpendicular to the radialconfining ring. Obviously, this will cause an appreciable and, perhaps,even greater setting expansion vertically with practically no expansionradially. Distortion is bound to take place under such circumstances.Furthermore, evenwhen the setting expansion is permitted to take placeevenly by the cushioning effect of a strip of asbestos inside the ring,there will still be distortion when the investment pushes against theinside surfaces of patterns such as M. O. D.s. It is now known thatinvestments show a slight rise in temperature upon setting andcomposition shown in curve I 2 under practical conditions will show arise in temperature of about 7 F. This will naturally expand the waxpattern and will do so to the extent of approximately 0.1%. Obviously,if the setting expansion was .l% there could be no possible distortion.This would be true to the utmost extent if the setting expansion andheat rise took place simultaneously and caused the wax to expand byheating exactly as much as the investment expanded on setting.

Curve l3 shows the setting expansion of the in vestment base used todevelop thermal expansion curve i0. This addition of 1.75% bariumchloride to this base composition decreased the setting expansionslightly as shown in curve It of Fig. 2. The addition of 1% of cadmia tothe latter composition then gives setting expansion curve I5 and it willbe seen that-this setting expansion seems to be ideal as explainedabove, since it is' very approximately 0.1%.

It thus seems that the ideal investment from all standpoints is obtainedin the composition utilizing barium chloride and cadmia as added to asimple investment composition base.

Since the reason for setting expansion taking place when a calciumsulfate binder is used is still unexplainable, it is impossible toreconcile the effectiveness of cadmia on investment compositions. .It isbelieved that the setting expansion is due to the growth of crystalsupon setting and also possibly upon somecolloidal phenomenon.

'ingly a logarithmic function rather than tory or glass and clay andtowhich an electrolyte has been added. It is probable that adsorptionplays an important part in this condition. The effect on dispersion ofthe solids, interfacial tension and particle adherence are undoubtedlyrelated to this phenomenon. Cadmia seems to raise the yield value andalso somewhat the mobility as referred to in ceramics. To maintain thesame consistency the W/P ratio must generally be raised about .01, thatis, it takes another cc. of water per 100 grams of powder. Since "thesetting andthermal expansions are unaffected in compositions such asshown by curve H due to this slight, raising of the W/P ratio, the onlyadverse effect is the-slight loss in compressive strength but this isgenerally overcome by the added increase in permeability.

The finer the particle size of cadmia the more viscous the investmentmix becomes and also the settingexpansion is additionally generallydecreased. In other words, the setting expansion canalso be'controlledby the particle size of the cadmia. The finer particle size does notseem to affect the thermal expansion so appreciably and a given weightof cadmia, regardless of particle size seems fairly equally effective.This indicates a straight chemical or' physico-chemical reaction and iscontrolled by the actual weight or weight percentage of cadmia present.

In both setting and thermal expansion effects, cadmia is most powerfulwhen used in smaller amounts. The first increment is more powerful thanthe second increment, etc. This is seema straight line arithmeticfunction.

Cadmia is generally a brown crystalline material that melts above 2550F.- although some authorities claim that it begins tochange com It isknown that many salts will decrease the setting expansion of calciumsulfate compositions, but so far no water insoluble and comparativelyinert material such as cadmia has been found that will have such apowerful effect; This or is especially advantageous in compositionswhere an excess of soluble salts areundesirable. Soluble salts oftencause surface efilorescence and under most conditions change the settingtime considerably. Cadmia does not show eitherof these disadvantages ,toany comparable extent and furthermore it will resist'heating to hightemperature where many salts, or perhaps most of them, will decompose.

When cadmia is mixed with investments, even' in small proportions, thereis a fairly marked change in consistency and working properties.

The mixture at the same W/P ratio will be stiller and resembles anaqueous suspension of refracposition slightly in the neighborhood of1800 F. It is available commercially as an extremely fine powder thatmay be amorphous or crystalline,

or a mixture of the two. It is used as a pigment in ceramics because ofits abilityto withstand high temperatures. It may be secured in thecrystalline form My heating the carbonate or nitrate, and can be wellcrystallized by long heating above a red heatwith or without a catalyst.Itmay'also be secured in comparatively large crystals by heating in theelectric furnace where the crystals will sublime. A fairly wellcrystallized material does not seem to change the setting time of manymixtures of investments appreciably, but the finest divided form mayshow an appreciable change. Again, this may be due to colloidalphenomena. Cadmia is reduced to the metal in the presence of carbon at ared heat and this is sometimes undesirable, but may be controlled by theproper ingredients and heating conditions.

Cadmia is a fairly inert material but on oc-" casion seems'to show someslight reaction with boric acid investments and also will liberate anoticeable amount of ammonia from investments containing ammoniumchloride and ammonium nitrate, for example. This is explained by thefact that it is somewhat soluble. in ammonium salts and acids. It isinsoluble in alkalis. Since every material 'is at least minutely solublein water, cadmia will perhaps give a slightly alkaline reaction, andthis. is why it changes theconsistency of the mix since alkalis, such aslime},

will generally act ina s'imilarfashion. f

It has been found that some of these properties of cadmia, that;is,' itseffects on-"the consistency and other properties may be changed thisfurther to about .1% more.

solution and then heated to give a homogeneous product. Cadmia and ironoxide will form a cadmium ferrite of the formula CdFezO4 .(CdOFeaOs).These mixtures sometimes slightly enhance the effectiveness of a givenpercent age of cadmia by possibly increasing the surface area of.thesame weight of'cadmia. These mixed oxides may also prevent reducingaction of other ingredients upon the cadmia, itself, or otherwise modifythe apparent colloidal phenomena.

It has been-found that some salt's will decrease the setting expansionof investments, some are apparently neutral in effect, and othersactually raise the setting expansions, some considerably. As specificexamples, the base compositions, as shown in curve l3, has asettingexpansion of 375%, 1% of cadmia will lower this to .14% and 5% ofcadmia will give a setting expansion of only .055%. Two percent of borlcacid will lower the expansion of the base to 215% and the addition of 1%of cadmia will give an expansion of -.02%. This is one of the few, andperhaps the first combination that will actually give a negativeexpansion in investments. With the same base, 1% of potassium iodidewill give a setting expansion of 22% and when a further addition of 1%of cadmia is made the setting expansion is reduced to .05%. Ammoniumchloride, when added in the amount of 1% reduces the setting expansionof the base to 28%, and an additional 1% of cadmia reduces it to .2%.

setting expansion is desired, such composition is possible by adding 1%of cadmium chloride and 1% of cadmia to the same base.

One per cent ofcupric chloride will raise the settingexpansion of thebase to over 1.0% and the addition of 1% of cadmiaeven increases Fiveper cent does not appreciably affect thesetting expansion of the base,but the addition of 1% of cadmia lowers it to.2%. It is thus seen thatthere v is almost unlimited field forc'ontrol of setting expansion withthe use of cadmia. If a composition having a low setting expansion andeven a negative one is desired, cadmia-is perhaps the only material thatwill do this in the small amounts of 1%, and of course, large amountswill even decrease'lthe setting expansion further. Where unafiectedorhigh setting expansions are desired, cadmia, when it has tov be usedto help the thermal expansion, etc., will nothinder the settingexpansion, and thus the range of setj ting expansion between a shrinkageand apositive expansion of over 1% is possible.

As a general rule, the alkali salts reduce the setting expansion, andcadmia enhances this effect. The alkaline earth salts do not reduce thesetting expansion so much, but cadmia is still effective in reducing thesetting expansion. The other metallic salts, especially those that I areof fairly heavy specific gravity, with cadmium .If the cadmia of anextremely fine grade parand copper as examples, the setting expansion isnot appreciably reduced, or actually increased, and cadmia is not so:effective in changing this sometimes desirable property. No strict rulecan as yet be set down, since, as. mentioned above, the

As remarked above, with barium chloride as an example, cadmia greatlyenhances the thermal expansion and materially lowers the settingexpansion and thus compositions with high thermal and low settingexpansion are made possible for the first time, and of course the rangesand combinationsof thermal expansiomand setting expansion are increasedmany fold and without impairing other desirable properties, such asset-- ting time, contamination of castings, strength,

etc.

In order to improve the surface of the castings it is possible toincorporate materials into the investment that will reduce the surfacetension and thus permit the investment to makeperfect contact with thewax pattern. Alkyl- 'sulphates, etc., are examples of such materials.

Also they may be painted on the pattern and the investment painted onsoon thereafter. Likeof cadmia will begin to show its usual eflect, and

setting expansionof the base to .2% and the further addition of cadmialowers it to .075%. One per cent of ammonium nitrate reduces the settingexpansion' of the base to 34% and the addition of 1% of-cadmia lowersthis considerably to .065%. r

One per cent of cupric nitrate, for example, again increases the settingexpansion of the base to .5% and 1% cadmia does not affect this figure.

One per cent of nickel chloride, for exampl as replacing all or wise,they may be added to the powdered portion of the investment or to thewater with which the investment is gaged. This is, of course, true ofall the materials used and described. They may be added to the water orto the powder or divided among the two so able results. Stronglyhygroscopic materials should preferably be added to the gaging water.

,Some finely divided solids and refractories aid somewhat in improvingthe surface of the mold, for example, titanium dioxide. Extremely finelydivided quartz and zircon are also advantageous for this purpose. Theuse of these finely divided materials generally raises the WI? ratiosomewhat and also affects the permeability. In this connection it mightbe'stated that an even grind of refractory will give greater.permeability than a particularly selected group of very fine, fines. andcoarser materials, the latter combination, however, increases thestrength.

Wherever it is desired to have expansions in excess of 1.25% at theusual casting temperature of 1300 F., it is advantageousto usecristobalite part of the quartz. Using 69% of cristobalite instead of69% of quartz, curve l2, could be raised to 2% or possibly above Thiswill vary depending upon the exact grade as to give most desir-- orcristobalite used. It seems that cristobalite made at highertemperatures and held for a longer period of time will give greaterexpansion and is generally preferable, although in some cases the use ofcatalysts, such as sodiumsilicate will lower the temperature ofcristobalite formation andthus enhance its expansion properties.

It is, of ,course, possible to substitute only a portion of cristobaliteand secure investments that will expand between 1.25% and 1.5%, forexample.

Spodumene may be added .as all or part of the filler and will giveunusually high expansions, even approaching and higher, but this willtake place generally around 1800 F. unless proper catalysts are addedthereto, as disclosed in copending application, Serial No. 309,784 flledDe-' cember 18, 1939.

It has been found that fora chloride investment, such as that whichdeveloped curve ll, powdered metallic copper will enhance the thermalexpansion properties when used in sufficient amounts. The copper,however, will not notice ably change the setting expansion and thus hasonlyone of the two desirable features, cadmia having both of them. Ofcourse, mixtures ofup to about 1%. Between 1 and 5% the effect .is alsoconsiderable but begins to diminish after that. The other cadmiacompounds, as mentioned above, are also most effective in smalleramounts although not as strong as cadmia and their upper limits arealso,-perhaps, lower, since the metal, for example, would melt andvaporize unless held under oxidizing conditions and other compounds mayalso be somewhat disadvantageous due to the inherent qualities of thecom'-' pound. I r

Some expansion improving agents will enable the production ofinvestments with comparatively high thermal expansions and with a' veryminicadmia and copper can be used wherever desirable.

. increased setting expansion due to the hygroscopic expansion is now nolonger so deleterious Under conditions wherein more setting expanto thepattern and will take place both radially and vertically to the sameextent, since the asbestos acts as a cushion.

As mentioned above, hundreds of experiments have shown that everysoluble salt tested increased the thermal expansion at least to somedegree and hereinafter the term expansion improving agents will be usedand shall be construed to include any and all of the soluble salts thatwill increase the thermal expansion of an form or another as thebinder.

-In many cases, cadmia will cause the setting expansion to reach itsfinal value in a minimum time. For example, curve 15 reached its upperexample, is to carve the wax pattern either on -investment containingcalcium sulphate in one mum of filler and, in fact, the nitratesandiodides will permit the use ofv straight alpha-gypsum,

' also boric acid has some advantageflinthese compositions. -By addingcadmia to these, the material may be used as a die and-castings may be'made directly into or onto them. Obviously, for die-making purposes lowsetting expansion is desirable and with cadmia and boric acid, forexamples, neutral or zero setting expansion is possible.

These compositions will be known as die casting compositions.

The die casting composition may be used to form a section of the moldand the balance of the mold may be made of another and softercomposition, such as one of the investment compositions describedherein. Furthermore, when using this type of die casting composition,the wax pattern need not necessarily be removed by heating themold tohigh temperatures sufficient to carbonize and vaporize.the wax. The waxmay be removed at .low temperatures by melting it or dissolving it outwith a suitable solvent. The metal or alloy may be cast into thesecompositions while the mold is at a comparatively low temperature.

The general procedure for casting inlays, for

the tooth in the mouth or on a die, reproduced into an impression takenfrom the tooth. In either case, the wax pattern is removed and encasedin an investment. It would speed up the process if it.were possible. totake an impression of the tooth cavity in wax, and without carving theouter contour, remove it from the tooth and form a die in the innersurface to the inner setting expansion limit in an hour whereas the samecomposition without the cadmia showed a slight setting expansionincrease even after. 24 hours and a considerable increase between oneand two hours. Obviously, this means that a mold will not changedimensions after about an hour with the composition as shown in curve l5and, therefore, no distortion can take place thereafter, also castingsmade at any time after one hour will be the same in dimensions. Some fewmaterials, for example, boric acid, are powerful fluxes and will cause ashrinkage in an investment at temperatures such as 1400 F. or above dueto-their chemical reaction or fluxing with the other ingredients. Inthis case cadmia will not prevent this inherent type of decomposition.

Other cadmium compounds such as the metal itself, the carbonate, etc.,that decompose or oxidize to leave the oxide at the casting temperaturewill also generally, however, affect the setting expansion,

give much of the desirable properties imparted by cadmia itself. Theywill not cavity, and thence carvethe outer contour of the -wax patternwhile still on the die and, thence,

withoutv removing it, enclose the outer side with investment and castsame. This would eliminate removal of the wax pattern from the die andthe necessity of lubrication, and possible distortion, upon removal.Heretofore, investment compositions were too soft, especially on thesurface, to permit accurate margin carving. a

Such die casting compositions, asthey will be called; may be made byconsiderably increasing the binder or calcium sulfate and thus produceharder dies. The difficulty .lies in-securing adequate thermal expansionand preferably without unduly high setting expansion. Thesedifiiculties'may beovercome by using the proper expansion improvingagentjsuch as, for example, chlorides, bromides, iodides, andnitrates.These increase the, thermal expansion considerably and make it possibleto use from to approximately 99% .binder, and still get expansions inthe neighborhood of 1.0 to 1.25%. Cristobalite is perhaps preferablewhen it is desired to get the most expansion with the least amount of Byusing such compositions and adding theretosome cadmia, it is possible toenhance the' refractoriness, that is, ability to withstand highertemperatures without shrinking and especially to lower the settingexpansion to .1% which otherwise, in some cases, would be in theneighborhood of .5% to .6% and would easily distort the wax pattern.

By using practically pure calcium sulfate and 0.1% to 5.% of boric acidin addition to such expansion reducing agents as Rochelle salts andpotassium sulfate, or mixtures thereof, it is possible to produce veryhard die compositions of excellent surface hardness, and with settingexpansions in the neighborhood of .05% to .l%. Such compositions do notwithstand high heating but form excellent dies and counter-dies at roomtemperature and may be heated to about 500 to 600 F. and are thereforeuseful for casting such metals as low fusing alloys, etc., that formvery valuable and extremely accurate dies and sectional dies forproducing intricate wax patterns from which castings are later made. Byadding approximately 1% or a fraction of a percent of cadmia, it ispossible to lower the setting expansion to a neutral or zero value andeven to give negative setting expansion properties wherever such aredesirable.

These latter die compositions thus have such useful properties as toenable them to serve many other and obvious purposes. They. may beuseful for holding such materials as plate glass when polishing thelatter. Also, the unusually high compressive strength surface hardness,combined with a substantially neutral or zero setting expansion', makethem advantageous as patterns, in conjunction with the die sinkingmachine.

The above mentioned compositions may also be used to hold objects in.place or to'cement materials of a brittle or fragile nature and where anintervening layer of expanding cement would crack same.

By using neutral soluble salts along with cadmia, it is possible toreduce the setting expansion to practically a neutral value and yetproduce objects .which are difficult of production now,

may be reduced to 10% and, in rare cases, somewhat lower, the uppervalue is about 55%, possibly 60%. By using additional amounts of calciumsulfate, it becomes a difierent type of composition, much stronger, andserves additional purposes. The calcium sulfate contents of these diecasting compositions varies from about 60% to approximately 95%. Diesfor lower temperature work, especially, consist practically entirely ofcalcium sulfate and, with proper additions of soluble salts and cadmia,these compositions have their properties enhanced and become moreuseful. These die compositions refer to those compositions havingapproximately 95% or more of caiciiiln sulfate.

In all of these compositions, which may be called molds and/or dies, therefractoriness is generally increased by increasing the amount ofrefractory filler, and the strength is increased by the increased amountof calcium sulfate and binder. With the soluble salts mentioned asparticularly good examples and with cadmia, the range of useful die andmold compositions containing calcium sulfate is widened considerably.

All of the cementitious compositions herein mentioned may be referred toas molds and dies and contain as the binder, calcium sulfate which,

in turn, has its properties improved by the addition of soluble saltsand further improved and a wide range of control given thereto bycaldmia.

What is claimed is:

1. A composition comprising 20 to 50% calciuin sulfate binder, 50 tofiller, and .05 to 10% of cadmia.

2. A composition for making molds or dies for use in forming or castingmetals, alloys and other materials and containing a calcium sulfatebinder, and having present in the composition a cadmia compound such asmetal, carbonate and organic salts and being capable of forming .05

to 10% cadmium oxide upon heating.

3. A composition for making molds or dies for use in forming or castingmetals, alloys and other materials, said'composition. including acalciumsulfate binder, .1 to 5% of a solublesalt as an expansion improvingagent, and .05 to 10% of cadmia.

4. A composition for making molds or dies for use in forming or castingmetals, alloys and other materials, said composition including a calciumsulfate binder, 1.0% of a soluble salt as an expansion improving agent,and .05 to 10% ofcadmia.

5. A composition for making molds or dies for use in forming or castingmetals, alloys and other materials and comprising 50 to 80% filler, 20to 50% calcium sulfate binder, .1 to 5% of a soluble salt as anexpansion improving agent, and .05 to 10% of cadmia.

6. A composition suitable for making molds or dies for use in forming orcasting metals, alloys and other materials which has a calcium sulfatebinder, .1 to 5% of soluble chloride, and .05 to 10% of cadmia. I

v 7. A composition suitable for making molds or dies for use in formingor casting metals, alloys and. other materials which has a calciumsulfate binder, .1 to 5% of barium chloride, and .05 to 10% of cadmia.

8. A composition suitable for making molds or dies for use in forming orcasting metals, alloys and other'materials which has a calcium sulfatebinder, .1 to 5% of barium chloride, and 1% of cadmia.

9. A composition suitable for making molds or dies for use in forming orcasting metals, alloys and other materials which has a calcium sulfatebinder, .1 to 5% of boric acid, and .05 to 10% of cadmia.

10. A composition suitable for making molds or dies for use in formingor casting metalsr alloys and other materials which has a calcium ofcadmia. 5

ROBERT NEIMAN.

